One of the ultimate ways to conserve water for thermoelectric power plants, nuclear power plants, concentrating solar power (CSP) plants, or centralized air conditioning/refrigeration systems is dry cooling. However, significant fan power consumption and significantly increased construction costs may inhibit dry cooling from commercial adoption. It has been estimated that, for a power plant, the dry cooling power consumption (primarily fan power consumption) could be up to 10% of the total power production of the power plant under hot weather conditions. The construction cost of a dry cooling facility for a 500 MW power plant could be up to five times higher than the cost of a wet-cooling tower.
The current approaches to achieve power plant dry cooling include compact condenser designs, micro tube heat exchangers for power plant condensers, dry and parallel condensing systems, and power plant heat rejection systems incorporating thermos-syphon cooler (TSC) technology. However, many of the approaches mentioned above may incur significant fan power consumption. In general, the heat transfer coefficient associated with airflow may be three orders of magnitude lower than that associated with a water flow due to a low air density. As a result, a large airflow volume is required for the dry cooling, which would incur exceedingly high fan-power consumption to circulate required airflow volume.
Under the condition of neglecting the thermal resistance from the cooling water to the interior surface of the container and that across the container wall, the well-known Newton's Law of cooling may be used to analyze the heat transfer from the condenser cooling water of a power plant or an air-conditioning/refrigerator system to the ambient air in terms of a dry cooling system:Q=AhΔT where, Q is the heat transfer rate from the cooling water to the ambient air, A is the total heat transfer surface area, h is the heat transfer coefficient, and ΔT is the mean temperature difference between the cooling water and the ambient air. It may be seen from the above equation that to promote the heat transfer rate, three approaches may be employed: increasing the heat transfer surface area; increasing the heat transfer coefficient; or increasing the temperature difference. However, the ambient air temperature cannot be controlled and the heat transfer surface temperature is limited by the cooling water temperature that cannot be too high above the ambient temperature, which leaves the other two choices as the variables for an increased heat transfer rate. It is well known that the heat transfer coefficient, h, is predominantly determined by the flow speed of the air relative to the heat transfer surface. To attain a high air velocity, large fan-power consumption is needed. Free or natural convection does not consume power, but its heat transfer coefficient is generally very low. However, it is believed that a combination of an increased heat transfer surface area and the enhanced free convection heat transfer coefficient may adequately remove the heat from the condenser without incurring significant fan-power consumption. Additionally, solar energy may be employed to enhance the airflow for a higher heat removal rate from the condenser. Similarly, the steam or vapor inside a condenser may be directly condensed using the aforementioned approach without involving the use of condenser cooling water.